Effects of Natural Organic Matter on Heavy Metal Transport during Infiltration

Washington State, like many others, has begun a program to dispose of highway runoff in which a priority has been given to the use of infiltration technologies (e.g., infiltration basins, dry wells, etc.). Heavy metals are of particular interest, because they are the most prevalent priority pollutant in highway runoff. Though traditionally these heavy metals are thought to possess relatively large retardation factors within the subsurface, previous studies have indicated a possibility of their transport being facilitated through complexation with natural organic matter (NOM). If ignored, this form of transport may pose serious errors in the prediction of metal breakthrough times and mass loadings to underlying groundwaters. In addressing this issue, large-scale soil columns are tested under loading conditions similar to actual infiltration best management practices to assess the performance of these facilities in removing heavy metals (Cd, Cu, Pb, Zn) from infiltrating water. Experiments were performed investigating the effects of high and low concentrations of NOM on metals attenuation by field soils. Results show that high concentrations of NOM actually improved soil column attenuation of the metals.